Ignition Timing Control (Me-SFI)
Engines are equipped with a double ignition system. Two spark plugs per cylinder are used. Each spark plug is controlled separately by the ME-SFI control module. Two ignition coils for one cylinder are integrated into one double coil. Spark plug cable connections are identified by an "a" or "b" stamped onto coil pack and valve cover. Spark plugs are fired in the following sequence: A-B, B-A, A-B, B-A, etc. See Fig 1 .
The spark plugs are fired independently to permit infinite variation in combustion timing. The ME-SFI control module can retard timing up to 14.5 degrees. The control module can also adjust spark plug ignition phasing (timing between both spark plugs firing on same cylinder) down to zero degrees (simultaneous firing). When engine is operating at partial load up to approximately 2000 RPM, both spark plugs are fired simultaneously. When engine is operating at medium and higher loads, spark plug firing are offset by up to 10 degrees. During this offset firing, spark plug actuation is alternated continuously to ensure uniform spark plug wear and prevent deposits on one side of the combustion chamber.